The present invention relates to an alkaline cell and, more particularly, to an improvement in an anode of an alkaline cell.
In a conventional alkaline cell such as an alkaline manganese cell, a silver oxide cell or a zinc air cell, a zinc powder is used to increase the reaction area of the anode and is amalgamated so as to increase a hydrogen overvoltage and to prevent the generation of hydrogen gas. However, since the surface area is large, the amount of mercury required is 5 to 10% by weight based on the weight of the zinc powder. In a large size alkaline cell such as an LR20, LR14 or LR6 (JIS), the amount of mercury per cell is also increased, since the amount of zinc used for the anode is large.
To reduce the amount of mercury which may pollute the environment, to prevent corrosion of zinc in an alkaline electrolyte so as to prevent generation of hydrogen gas, and to prevent leakage of the electrolyte, it has been proposed to add various metals to zinc.
For example, Japanese Patent Disclosure No. 52-74833 discloses the use of a zinc powder coated with an indium (In)-mercury (Hg) alloy for the anode. Japanese Patent Disclosure No. 53-30741 discloses the use of a zinc powder coated with a gallium (Ga)-indium (In)-mercury (Hg) alloy for the anode.
In Japanese Patent Disclosure No. 53-103127, it is proposed to coat a zinc powder with a mercury amalgamated alloy of indium (In), gallium (Ga), or a mixture thereof. The amount of indium or gallium used is 2 to 10% by weight based on the weight of zinc, while the amount of mercury used is 2 to 14% by weight based on the weight of zinc.
Japanese Patent Disclosure No. 53-41733 also discloses coating of a zinc powder with tantalum alone or tantalum alloys such as Ta-Ga and Ta-In, after their amalgamation with or without a small amount of mercury. This prior art does not disclose the particular amount of mercury.
Furthermore, Japanese Patent Disclosure No. 47-35727 proposes an alkaline cell which uses an anode obtained by amalgamating with 10% by weight of mercury a zinc alloy containing gallium (Ga), lead (Pb), or germanium (Ge).